Dinoflagellate Genus Dinophysis Research Articles

Advances in the Early Warning of Shellfish Toxification by Dinophysis acuminata.

In Western Europe, the incidence of DST is likely the highest globally, posing a significant threat with prolonged bans on shellfish harvesting, mainly caused by species of the dinoflagellate genus Dinophysis. Using a time series from 2014 to 2020, our study aimed (i) to determine the concentration of D. acuminata in water at which shellfish toxin levels could surpass the regulatory limit (160 µg OA equiv kg-1) and (ii) to assess the predictability of toxic events for timely mitigation actions, especially concerning potential harvesting bans. The analysis considered factors such as (i) overdispersion in the data, (ii) distinct periods of presence and absence, (iii) the persistence of cells, and (iv) the temporal lag between cells in the water and toxins in shellfish. Four generalized additive models were tested, with the Tweedie (TW-GAM) model showing superior performance (>85%) and lower complexity. The results suggest existing thresholds currently employed (200 and 500 cells L-1) are well-suited for the Portuguese coast, supported by empirical evidence (54-79% accuracy). The developed algorithm allows for thresholds to be tailored on a case-by-case basis, offering flexibility for regional variations.

De novo transcriptome assembly and gene annotation for the toxic dinoflagellate Dinophysis

Species within the dinoflagellate genus Dinophysis can produce okadiac acid and dinophysistoxins leading to diarrhetic shellfish poisoning. Since the first report of D. ovum from the Gulf of Mexico in 2008, reports of other Dinophysis species across US have increased. Members of the D. cf. acuminata complex (D. acuminata, D. acuta, D. ovum, D. sacculus) are difficult to differentiate due to their morphological similarities. Dinophysis feeds on and steals the chloroplasts from the ciliate, Mesodinium rubrum, which in turn has fed on and captured the chloroplasts of its prey, the cryptophyte Teleaulax amphioxeia. The objective of this study was to generate de novo transcriptomes for new isolates of these mixotrophic organisms. The transcriptomes obtained will serve as a reference for future experiments to assess the effect of different abiotic and biotic conditions and will also provide a useful resource for screening potential marker genes to differentiate among the closely related species within the D. cf. acuminata-complex. The complete comprehensive detailed workflow and links to obtain the transcriptome data are provided.

Mortality and histopathology in sheepshead minnow (Cyprinodon variegatus) larvae exposed to pectenotoxin-2 and Dinophysis acuminata

Toxic species of the dinoflagellate genus Dinophysis can produce diarrheic toxins including okadaic acid (OA) and dinophysistoxins (DTXs), and the non-diarrheic pectenotoxins (PTXs). Okadaic acid and DTXs cause diarrheic shellfish poisoning (DSP) in human consumers, and also cause cytotoxic, immunotoxic and genotoxic effects in a variety of mollusks and fishes at different life stages in vitro. The possible effects of co-produced PTXs or live cells of Dinophysis to aquatic organisms, however, are less understood. Effects on an early life stage of sheepshead minnow (Cyprinodon variegatus), a common finfish in eastern USA estuaries, were evaluated using a 96-h toxicity bioassay. Three-week old larvae were exposed to PTX2 concentrations from 50 to 4000 nM, live Dinophysis acuminata culture (strain DAVA01), live cells resuspended in clean medium or culture filtrate. This D. acuminata strain produced mainly intracellular PTX2 (≈ 21 pg cell−1), with much lower levels of OA and dinophysistoxin-1.No mortality or gill damages were observed in larvae exposed to D. acuminata (from 5 to 5500 cells mL−1), resuspended cells and culture filtrate. However, exposure to purified PTX2 at intermediate to high concentrations (from 250 to 4000 nM) resulted in 8 to 100% mortality after 96 h (24-h LC50 of 1231 nM). Histopathology and transmission electron microscopy of fish exposed to intermediate to high PTX2 concentrations revealed important gill damage, including intercellular edema, necrosis and sloughing of gill respiratory epithelia, and damage to the osmoregulatory epithelium, including hypertrophy, proliferation, redistribution and necrosis of chloride cells. Tissue damage in gills is likely caused by the interaction of PTX2 with the actin cytoskeleton of the affected gill epithelia. Overall, the severe gill pathology observed following the PTX2 exposure suggested death was due to loss of respiratory and osmoregulatory functions in C. variegatus larvae.

Dinophysis Ehrenberg (Dinophyceae) in Southern Chile harbours red cryptophyte plastids from Rhodomonas/Storeatula clade

Photosynthetic species of the dinoflagellate genus Dinophysis are known to retain temporary cryptophyte plastids of the Teleaulax/Plagioselmis/Geminigera clade after feeding the ciliate Mesodinium rubrum. In the present study, partial plastid 23S rDNA sequences were retrieved in Southern Chilean waters from oceanic (Los Lagos region), and fjord systems (Aysén region), in single cells of Dinophysis and accompanying organisms (the heliozoan Actinophrys cf. sol and tintinnid ciliates), identified by means of morphological discrimination under the light microscope. All plastid 23S rDNA sequences (n = 23) from Dinophysis spp. (Dinophysis acuta, D. caudata, D. tripos and D. subcircularis) belonged to cryptophytes from clade V (Rhinomonas, Rhodomonas and Storeatula), although they could not be identified at genus level. Moreover, five plastid sequences obtained from heliozoans (Actinophryida, tentatively identified as Actinophrys cf. sol), and tintinnid ciliates, grouped together with those cryptophyte sequences. In contrast, two additional sequences from tintinnids belonged to other taxa (chlorophytes and cyanobacteria). Overall, the present study represents the first time that red cryptophyte plastids outside of the Teleaulax/Plagioselmis/Geminigera clade dominate in wild photosynthetic Dinophysis spp. These findings suggest that either Dinophysis spp. are able to feed on other ciliate prey than Mesodinium and/or that cryptophyte plastids from clade V prevail in members of the M. rubrum species complex in the studied area.

Cultures of Dinophysis sacculus, D. acuminata and pectenotoxin 2 affect gametes and fertilization success of the Pacific oyster, Crassostrea gigas

Harmful algal blooms (HABs) of toxic species of the dinoflagellate genus Dinophysis are a threat to human health as they are mainly responsible for diarrheic shellfish poisoning (DSP) in the consumers of contaminated shellfish. Such contamination leads to shellfish farm closures causing major economic and social issues. The direct effects of numerous HAB species have been demonstrated on adult bivalves, whereas the effects on critical early life stages remain relatively unexplored. The present study aimed to determine the in vitro effects of either cultivated strains of D. sacculus and D. acuminata isolated from France or their associated toxins (i.e. okadaic acid (OA) and pectenotoxin 2 (PTX2)) on the quality of the gametes of the Pacific oyster Crassostrea gigas. This was performed by assessing the ROS production and viability of the gametes using flow cytometry, and fertilization success using microscopic counts. Oocytes were more affected than spermatozoa and their mortality and ROS production increased in the presence of D. sacculus and PTX2, respectively. A decrease in fertilization success was observed at concentrations as low as 0.5 cell mL−1 of Dinophysis spp. and 5 nM of PTX2, whereas no effect of OA could be observed. The effect on fertilization success was higher when both gamete types were concomitantly exposed compared to separate exposures, suggesting a synergistic effect. Our results also suggest that the effects could be due to cell-to-cell contact. These results highlight a potential effect of Dinophysis spp. and PTX2 on reproduction and recruitment of the Pacific oyster.

Relations between optical properties, dinoflagellates and zooplanktonic crustaceans in Antofagasta Bay (23°S, Chile)

Abstract Antofagasta Bay is characterized by a high primary productivity due to the presence of the cold Humboldt Stream that is associated with a high diversity in flora and fauna in the benthic and pelagial environments of the Chilean west coast. Nevertheless, due to the global climate changes, the existing biodiversity patterns change as well. The aim of the present study was to analyse Antofagasta Bay for determining the existence of patterns between optical properties of the water, and the phytoplankton and zooplankton. The results show that one site had high chlorophyll concentrations, high reflectance, a high abundance of the dinoflagellate genus Dinophysis, and a high abundance of copepodites, whereas five sites had low chlorophyll concentrations, a low reflectance value, low copepodite abundances, and high abundances of dinoflagellates of the genera Ceratium, Gymnodinium and Prorocentrum. These results are similar to earlier observations for the coastal waters along northern Chile.

Occurrence of Marine Biotoxins and Shellfish Poisoning Events and Their Causative Organisms in Argentine Marine Waters

In the Argentine Sea, marine phycotoxins of microalgal origin associated with five shellfish poisoning syndromes have been reported. The most problematic in terms of toxicity and geographic distribution is paralytic shellfish poisoning (PSP), followed by diarrhetic shellfish poisoning (DSP). In contrast, amnesic shellfish poisoning (ASP), spiroimine shellfish poisoning (SSP), and azaspiracid shellfish poisoning (AZP) have not been reported to cause human illness or closures of shellfish harvest sites in Argentina to date but pose a potential risk, as associated toxins and producing organisms are present in Southwest Atlantic waters and were detected at subregulatory levels in mollusks. Alexandrium catenella and Gymnodinium catenatum have been identified as producers of the PSP toxins C1/2, gonyautoxins (GTX1-4), saxitoxin (STX), and neosaxitoxin (NEO) in the Argentine Sea. Nine potentially toxigenic species of the diatom genus Pseudo-nitzschia have been reported for Argentinean coastal waters: P. australis, P. brasiliana, P. delicatissima, P. fraudulenta, P. multiseries, P. pseudodelicatissima, P. pungens, P. seriata, and P. turgidula, all of which are known to produce the neurotoxin domoic acid that causes ASP. Two genera have been identified as producers of DSP toxins in Argentina: the benthic dinoflagellate Prorocentrum lima and several species of the pelagic dinoflagellate genus Dinophysis: D. acuminata, D. caudata, D. fortii, D. norvegica, and D. tripos. The occurrence of these species in Argentine waters is associated with okadaic acid (OA), dinophysistoxin-1 (DTX-1), pectenotoxin-2 (PTX-2), and pectenotoxin-2 seco acid (PTX-2sa). Historically, yessotoxins (YTXs) were also included in DSP syndrome and all three known YTX-producers have been confirmed in Argentinean waters: Gonyaulax spinifera, Lingulodinium polyedra, and Protoceratium reticulatum, but of these only P. reticulatum could be associated with YTX production to date. Several species of the family Amphidomataceae, which cause AZP, have been reported for Argentina: Amphidoma languida, Azadinium dexteroporum, Az. luciferelloides, Az. poporum, and Az. spinosum. In Argentinean coastal waters, out of these species only Az. poporum has been identified as toxigenic to date, as it produces azaspiracid-2 (AZA-2) and its phosphorylated form. Currently in Argentina, seafood is monitored for the risk of ASP, AZP, DSP, and PSP.

Accumulation of Dinophysis Toxins in Bivalve Molluscs.

Several species of the dinoflagellate genus Dinophysis produce toxins that accumulate in bivalves when they feed on populations of these organisms. The accumulated toxins can lead to intoxication in consumers of the affected bivalves. The risk of intoxication depends on the amount and toxic power of accumulated toxins. In this review, current knowledge on the main processes involved in toxin accumulation were compiled, including the mechanisms and regulation of toxin acquisition, digestion, biotransformation, compartmentalization, and toxin depuration. Finally, accumulation kinetics, some models to describe it, and some implications were also considered.

Dinophysis acuta in Scottish Coastal Waters and Its Influence on Diarrhetic Shellfish Toxin Profiles.

Diarrhetic shellfish toxins produced by the dinoflagellate genus Dinophysis are a major problem for the shellfish industry worldwide. Separate species of the genus have been associated with the production of different analogues of the okadaic acid group of toxins. To evaluate the spatial and temporal variability of Dinophysis species and toxins in the important shellfish-harvesting region of the Scottish west coast, we analysed data collected from 1996 to 2017 in two contrasting locations: Loch Ewe and the Clyde Sea. Seasonal studies were also undertaken, in Loch Ewe in both 2001 and 2002, and in the Clyde in 2015. Dinophysis acuminata was present throughout the growing season during every year of the study, with blooms typically occurring between May and September at both locations. The appearance of D. acuta was interannually sporadic and, when present, was most abundant in the late summer and autumn. The Clyde field study in 2015 indicated the importance of a temperature front in the formation of a D. acuta bloom. A shift in toxin profiles of common mussels (Mytilus edulis) tested during regulatory monitoring was evident, with a proportional decrease in okadaic acid (OA) and dinophysistoxin-1 (DTX1) and an increase in dinophysistoxin-2 (DTX2) occurring when D. acuta became dominant. Routine enumeration of Dinophysis to species level could provide early warning of potential contamination of shellfish with DTX2 and thus determine the choice of the most suitable kit for effective end-product testing.

Evolutionary transition towards permanent chloroplasts? - Division of kleptochloroplasts in starved cells of two species of Dinophysis (Dinophyceae).

Species within the marine toxic dinoflagellate genus Dinophysis are phagotrophic organisms that exploit chloroplasts (kleptochloroplasts) from other protists to perform photosynthesis. Dinophysis spp. acquire the kleptochloroplasts from the ciliate Mesodinium rubrum, which in turn acquires the chloroplasts from a unique clade of cryptophytes. Dinophysis spp. digest the prey nuclei and all other cell organelles upon ingestion (except the kleptochloroplasts) and they are therefore believed to constantly acquire new chloroplasts as the populations grow. Previous studies have, however, indicated that Dinophysis can keep the kleptochloroplasts active during long term starvation and are able to produce photosynthetic pigments when exposed to prey starvation. This indicates a considerable control over the kleptochloroplasts and the ability of Dinophysis to replicate its kleptochloroplasts was therefore re-investigated in detail in this study. The kleptochloroplasts of Dinophysis acuta and Dinophysis acuminata were analyzed using confocal microscopy and 3D bioimaging software during long term starvation experiments. The cell concentrations were monitored to confirm cell divisions and samples were withdrawn each time a doubling had occurred. The results show direct evidence of kleptochloroplastidic division and that the decreases in total kleptochloroplast volume, number of kleptochloroplasts and number of kleptochloroplast centers were not caused by dilution due to cell divisions. This is the first report of division of kleptochloroplasts in any protist without the associated prey nuclei. This indicates that Dinophysis spp. may be in a transitional phase towards possessing permanent chloroplasts, which thereby potentially makes it a key organism to understand the evolution of phototrophic protists.

Dinophysis Species Associated with Diarrhetic Shellfish Poisoning Episodes in North Patagonian Gulfs (Chubut, Argentina)

ABSTRACT The marine dinoflagellate genus Dinophysis Ehrenberg is globally distributed in coastal and oceanic waters and can produce lipophilic toxins. These toxins can accumulate in filter-feeding shellfish and cause diarrhetic shellfish poisoning (DSP). Between 2009 and 2011 the two most frequent and abundant Dinophysis species found in North Patagonian gulfs were Dinophysis tripos Gourret and Dinophysis acuminata Claparede and Lachmann, and in 2015 D. tripos was the only toxic species found in moderate to high relative abundances when mouse bioassay results for DSP were positive. The positive results from mouse bioassay for DSP agree with moderate to high relative abundances of D. tripos and it was the only potentially toxic Dinophysis species found in the samples. The toxin profiles consisted mainly of pectentoxin-2 (PTX-2) followed by PTX-11 and PTX-2 seco acid. The toxin profiles of the samples could be associated with D. tripos, because the maximum proportion of D. acuminata did not exceed 1.3% of t...

Acquired phototrophy in Mesodinium and Dinophysis – A review of cellular organization, prey selectivity, nutrient uptake and bioenergetics

Acquired phototrophy, i.e. the use of chloroplasts from ingested prey, can be found among some species of dinoflagellates and ciliates. The best studied examples of this phenomenon in these groups are within the ciliate genus Mesodinium and the dinoflagellate genus Dinophysis, both ecologically important genera with a worldwide distribution. Mesodinium species differ considerably in their carbon metabolism. Some species rely almost exclusively on food uptake, while other species rely mostly on photosynthesis. In Mesodinium with acquired phototrophy, a number of prey organelles in addition to chloroplasts may be retained, and the host ciliate has considerable control over the acquired chloroplasts; Mesodinium rubrum is capable of dividing its acquired chloroplasts and can also photoacclimate. In Dinophysis spp., the contents of ciliate prey are sucked out, but only the chloroplasts are retained from the ingested prey. Some chloroplast house-keeping genes have been found in the nucleus of Dinophysis and some preliminary evidence suggests that Dinophysis may be capable for photoacclimation. Both genera have been claimed to take up inorganic nutrients, including NO3−, indicating that processes beyond photosynthesis have been acquired. M. rubrum seems to depend upon prey species within the Teleaulax/Plagioselmis/Geminigera clade of marine cryptophytes. Up until now, Dinophysis species have only been maintained cultured on M. rubrum as food, but other ciliates may also be ingested. Dinophysis spp. and M. rubrum are obligate mixotrophs, depending upon both prey and light for sustained growth. However, while M. rubrum only needs to ingest 1–2% of its carbon demand per day to attain maximum growth, Dinophysis spp. need to obtain about half of their carbon demand from ingestion for maximum growth. Both Mesodinium and Dinophysis spp. can survive for months in the light without food. The potential role for modeling in exploring the complex balance of phototrophy and phago-heterotrophy, and its ecological implications for the mixotroph and their prey, is discussed.

Production and excretion of okadaic acid, pectenotoxin-2 and a novel dinophysistoxin from the DSP-causing marine dinoflagellate Dinophysis acuta – Effects of light, food availability and growth phase

Diarrhetic shellfish poisoning (DSP) toxins constitute a severe economic threat to shellfish industries and a major food safety issue for shellfish consumers. The prime producers of the DSP toxins that end up in filter feeding shellfish are species of the marine mixotrophic dinoflagellate genus Dinophysis. Intraspecific toxin contents of Dinophysis spp. vary a lot, but the regulating factors of toxin content are still poorly understood. Dinophysis spp. have been shown to sequester and use chloroplasts from their ciliate prey, and with this rare mode of nutrition, irradiance and food availability could play a key role in the regulation of toxins contents and production. We investigated toxin contents, production and excretion of a Dinophysis acuta culture under different irradiances, food availabilities and growth phases. The newly isolated strain of D. acuta contained okadaic acid (OA), pectenotoxins-2 (PTX-2) and a novel dinophysistoxin (DTX) that we tentatively describe as DTX-1b isomer. We found that all three toxins were excreted to the surrounding seawater, and for OA and DTX-1b as much as 90% could be found in extracellular toxin pools. For PTX-2 somewhat less was excreted, but often >50% was found extracellularly. This was the case both in steady-state exponential growth and in food limited, stationary growth, and we emphasize the need to include extracellular toxins in future studies of DSP toxins. Cellular toxin contents were largely unaffected by irradiance, but toxins accumulated both intra- and extracellularly when starvation reduced growth rates of D. acuta. Toxin production rates were highest during exponential growth, but continued at decreased rates when cell division ceased, indicating that toxin production is not directly associated with ingestion of prey. Finally, we explore the potential of these new discoveries to shed light on the ecological role of DSP toxins.

The marine dinoflagellate genus Dinophysis can retain plastids of multiple algal origins at the same time

The ‘phototrophic’ Dinophysis Ehrenberg species are well known to have plastids of a cryptophyte origin, more specifically cryptophyte genus complex Teleaulax/ Geminigera. However, how often the phototrophic Dinophysis could retain both types of plastids from this genus complex at the same time in a cell and also whether the phototrophic cells could retain plastids of the other algal origins rather than cryptophyte have not been investigated in detail. We isolated a total of 67 phototrophic Dinophysis spp. cells between May 2008 and September 2009 along western and southern coasts of Korea and amplified psbA as a tracer to investigate plastid diversity from the isolated cells. Then, the PCR products were digested with a restriction enzyme, SfaNI, to distinguish between the most common Teleaulax amphioxeia-type and the less common T. acuta-type plastids. During this study, we sometimes encountered ‘green’ Dinophysis acuminata cells, which contained varying degree of red autofluorescencing green plastids inside the cell, along together typical orange autofluorescencing reddish-brown plastids. The RFLP patterns of the PCR products digested by SfaNI revealed that a total of 66 Dinophysis cells analyzed in this study all contained T. amphioxeia-type plastid. Further, approximately two-thirds of the analyzed Dinophysis cells contained both T. amphioxeia-type and T. acuta-type plastids at the same time in a single cell. Interestingly, SfaNI digestion of the products amplified on psbA gene from 10 Dinophysis cells produced a different RFLP pattern: in addition to T. amphioxeia-type and sometimes T. acuta-type plastid, undigested fragments occurred. We cloned the PCR products and determined psbA gene sequences from the cells containing undigested fragments with SfaNI. Surprisingly, these Dinophysis cells contained even three (i.e. cryptophytes T. amphioxeia and T. acuta and raphidophyte Heterosigma akashiwo) or four (i.e. cryptophytes T. amphioxeia and T. acuta, raphidophyte H. akashiwo, and chlorophyte Pyramimonas sp.) different plastid sequences at the same time in a single cell. Our result indicates that besides the sole prey Mesodinium rubrum (= Myrionecta rubra) known until now, there may be other potential prey organisms, presumably the plastid-retaining ciliates, from which phototrophic Dinophysis may acquire plastids of several algal origins other than cryptophyte.

Marine toxins and the cytoskeleton: pectenotoxins, unusual macrolides that disrupt actin

In recent years, many natural macrolactones have been found that display toxicity against the actin cytoskeleton. Pectenotoxins are macrolactones produced by species of the dinoflagellate genus Dinophysis. They were initially classified within the diarrheic shellfish poisoning group of toxins, because of their co-occurrence and biological origin, but mice toxicity assays demonstrated that pectenotoxins do not induce diarrheic symptoms. Intraperitoneal injection of pectenotoxins into mice produces high hepatotoxicity as the principal symptom, so the liver seems to be their target organ. Up to now, 15 pectenotoxin analogs have been discovered, with different toxicological potencies that are related to their structures. Now, it is generally accepted that the actin cytoskeleton is the principal molecular target of pectenotoxins. Although recent studies have demonstrated that pectenotoxins induce actin filament disruption by a capping effect, other kinds of activity, such as sequestration of actin, cannot be ruled out. All of the active analogs tested triggered disruption of the actin cytoskeleton and displayed potencies that correlated with their toxicity in mice. Moreover, pectenotoxins induce apoptosis to a higher degree in tumor cells than in normal cells of the same tissue. This fact opens the prospect of studying new chemotherapy agents and actin cytoskeleton dynamics with potential clinical applications.

First successful culture of the marine dinoflagellate Dinophysis acuminata

The dinoflagellate genus Dinophysis in- cludes several species that cause diarrhetic shellfish poi- soning, none of which have yet been established in cul- ture. We report on the maintenance of Dinophysis acuminata cultures that were established in December 2005 and also on its feeding mechanism, and growth rates when fed the ciliate prey Myrionecta rubra with and without the addition of the cryptophyte Teleaulax sp. D. acuminata grew well (growth rate of 0.95 d -1 ) in laboratory culture when supplied with the marine ciliate M. rubra as prey, reaching a maximum concentration of about 2400 cells ml -1 at the end of the feeding experiment. In contrast, D. acuminata did not show sustained growth in the absence of the ciliate or when provided the cryptophyte Teleaulax sp. as prey (D. acuminata used its peduncle to extract the cell contents of the prey organism, M. rubra). Based on the prey- preda- tor interactions occurring among D. acuminata, M. rubra, and Teleaulax sp. in this study, establishment of perma- nent culture of the dinoflagellate D. acuminata may facil- itate a better understanding of the ecophysiology, biol- ogy, and toxicology of Dinophysis species, as well as the evolution of dinoflagellate plastids.

Genetic analyses of Dinophysis spp. support kleptoplastidy

The question of whether the toxin-producing and bloom-forming dinoflagellate genus Dinophysis contains plastids that are permanent or contains temporary so-called kleptoplastids is still unresolved. We sequenced plastid 16S rRNA gene, the complete trnA gene and the intergenic transcribed spacer region located between the trnA gene and the 23S rRNA gene, and performed diagnostic PCR on cells of the genus Dinophysis. Dinophysis spp. were collected from five different geographical regions: the Baltic Sea, the North Sea, the Greenland Sea and the Norwegian fjord Masfjorden. In most cases the sequence analysis showed that the sequences were identical to each other and to sequences from the cryptophyte Teleaulax amphioxeia SCCAP K0434, regardless of the place of sampling or the species analyzed. The exception was some cells of Dinophysis spp. from the Greenland Sea. These contained a 16S rRNA gene sequence that was more closely related to the cryptophyte Geminigera cryophila. The cells of Dinophysis contained either one of the 16S rRNA gene sequences or both in the same cell. Our results challenge the hypothesis that the plastids in Dinophysis are permanent and suggest that they are more likely to be kleptoplastids.

Seasonal distribution of species of the toxic dinoflagellate genus Dinophysis in Maizuru Bay (Japan), with comments on their autofluorescence and attachment of picophytoplankton

The seasonal distribution of the dinoflagellate genus, Dinophysis, in Maizuru Bay, Japan, was investigated from May 1997 to December 1999. Seven species of Dinophysis were detected, including the toxic species of Dinophysis acuminata and D. fortii. The most dominant species was D. acuminata, detected year-around and more abundantly during periods when water temperatures were between 15 and 18 °C. No relationship was found between cell abundance of Dinophysis spp. and concentrations of dissolved inorganic nutrients. Phycoerythrin containing nano- and picophytoplankton (cryptophytes and cyanobacteria), suspected to be prey of mixotrophic Dinophysis, were enumerated simultaneously. A clear relationship was not found among the cell abundances of Dinophysis spp. and nano- and picophytoplankton. Autofluorescence of Dinophysis spp. (mainly D. acuminata and D. fortii) under blue-light excitation was usually of a yellow-orange color. Occasionally, Dinophysis spp. had red autofluorescencing and yellow-orange autofluorescencing particles. The proportion of cells possessing red autofluorescence tended to be higher in the warm season. Numerous coccoid cells of picophytoplankton (ca. 1–2 μm in diameter) were found attached to the cell surface of D. acuminata, D. fortii, etc. and food vacuole-like structures also observed. These observations suggest there is a close relationship between mixotrophic Dinophysis spp. and certain picophytoplankton. Based on our observations, the possibility that the picophytoplankton found to be attached onto Dinophysis cell surfaces are a food source for Dinophysis, and a source of DSP toxins, is discussed.

Molecular Evidence for Plastid Robbery (Kleptoplastidy) in Dinophysis, a Dinoflagellate causing Diarrhetic Shellfish Poisoning

The dinoflagellate genus Dinophysis contains species known to cause diarrhetic shellfish poisoning. Although most photosynthetic dinoflagellates have plastids with peridinin, photosynthetic Dinophysis species have cryptophyte-like plastids containing phycobilin rather than peridinin. We sequenced nuclear- and plastid-encoded SSU rDNA from three photosynthetic species of Dinophysis for phylogenetic analyses. In the tree of nuclear SSU rDNA, Dinophysis was a monophyletic group nested with peridinin-containing dinoflagellates. However, in the tree of plastid SSU rDNA, the Dinophysis plastid lineage was within the radiation of cryptophytes and was closely related to Geminigera cryophila. These analyses indicate that an ancestor of Dinophysis, which may have originally possessed peridinin-type plastid and lost it subsequently, adopted a new plastid from a cryptophyte. Unlike dinoflagellates with fully integrated plastids, the Dinophysis plastid SSU rDNA sequences were identical among the three species examined, while there were species-specific base substitutions in their nuclear SSU rDNA sequences. Queries of the DNA database showed that the plastid SSU rDNA sequence of Dinophysis is almost identical to that of an environmental DNA clone of a <10 pm sized plankter, possibly a cryptophyte and a likely source of the Dinophysis plastid. The present findings suggest that these Dinophysis species engulfed and temporarily retained plastids from a cryptophyte.

Dinophysis - a planktonic dinoflagellate genus which can act both as a prey and a predator of a ciliate

Heterotrophic members of the marine plankton dinoflagellate genus Dinophysis are specialized predators, whose food includes the prostomatid ciliate Tiarina fusus. This ciliate differs from most planktonic ciliates in its ability to ingest prey of its own size including autotrophic Dinophysis spp. However, when trying to catch a heterotrophic Dinophy- sis sp., the ciliate is trapped instead by the dinoflagellate and emptied via a feeding tube (peduncle), which originates from the flagellar pore of the dinoflagellate. The specific predation on a ciliate by a heterotrophic dinoflagellate represents a new trophic link in the marine planktonic food web. The existence of colourl.ess thecate dinoflagellates in the marine pelagial has been recognized among taxo- nomists for more than a century (Gaines & Elbrachter 1987). In spite of this, few ecological studies dealing with the marine planktonic food webs have included them in the protozoan plankton even though they may make up a substantial part of the biomass of this group (Smetacek 1981). Knowledge about their trophic role in